In manufacturing components for the aeronautical industry, especially for manufacturing structural elements of an aircraft, the use of composite materials formed by fabrics with an organic matrix, for example a thermoplastic resin, and continuous fibers, for example glass fiber- or carbon fiber-reinforced plastic (CFRP), oriented in one direction in one and the same ply or fabric is well known.
These composite materials are used both for manufacturing skin panels and for manufacturing stringers, which can be manufactured with different sections, for example with a T-shaped section, I-shaped section, L-shaped section, trapezoidal-shaped section, etc.
An aircraft skin structure, for example part of the fuselage or part of a wing, is conventionally formed by a skin panel and by a series of stringers co-bonded or co-cured to one of the faces of the panel to reinforce it. The stringers are arranged in the longitudinal direction with respect to said panel, and a series of transversely arranged ribs collaborating with the stringers to provide strength to the panels and to improve the stability under compression or shearing thereof are further incorporated.
One of the most common stringer profiles is the T-shaped profile, which is obtained by means of attaching two L-shaped profiles. The co-curing of composite materials consists of the joint curing of two or more parts inside a furnace without either of them having first gone through a prior curing process.
The possibility of incorporating reinforcements integrated in the web of the stringer as shown in FIG. 1 is known. A reinforcing element (17) consisting of a solid block obtained, for example, by means of unidirectional fibers is manufactured separately in those processes, such that in manufacturing the stringer a planar stack of fabrics (FIG. 2A) is used as the starting material, in which a channel (18, 19) (FIG. 2B) is formed by means of a bend in the sheet, within which bend the reinforcing element (17) (FIG. 2C) is placed. Finally, the profile is closed on itself, turning it into T-shaped by means of the suitable tool (FIG. 2D), and the assembly is cured, the reinforcement (17) being housed in the head of the web.
These known processes are used to provide reinforcement exclusively at the end of the head of the web, but not anywhere else in the stringer. Furthermore, as seen in the sequence of FIGS. 2 (A-D), it is necessary to greatly modify the process of manufacture and the necessary tool because the reinforcement must be manufactured separately, after placing the reinforcement in the plies to subsequently fold the profile.
The structural performance of the profile thus obtained is not completely effective because the reinforcing element is after all an independent body resulting from the basic stacking of plies. The reinforcement is housed inside the stringer, which means, as seen in FIGS. 1A and 1B, that the reinforcement does not extend up to the very edge of the head of the web, but rather that end is formed by the basic stacking of the stringer which is exposed to possible damage due to impact.
Current T-shaped profiles cannot have a reinforcement in the foot and another one in the web because with the current manufacturing technique there would be an unacceptable superposition of fabrics (as shown in FIG. 7) precisely in the area that is most prone to accumulating defects (porosities, resin accumulation, etc.), the radius or elbow of the stringer. As observed in said FIG. 7, to obtain reinforcements using the conventional manufacturing technique for manufacturing T-shaped stringers, the ends of the reinforcing fabrics of the web (9) would be superimposed on the ends of the reinforcing fabrics of the foot (10), which is not allowed by manufacturing standards.
On the other hand, a tool in the form of a mold that has to copy the shape of the profile is used in a final phase of manufacturing the stringers, and in the case of I-shaped or J-shaped profiles, the mold is complex because it has to provide stability to the “cantilever” of those profiles. Depending on the curvature of the panel where the foot rests and, given that the head of an I-shaped or J-shaped profile is perpendicular to the web, the male mold can have demolding problems.